We propose to synthesize and test a new series of peptides to be used in our studies of the activation of lecithin:cholesterol acyltransferase (LCAT). The two tests involved are the activation of LCAT by synthetic peptides and the measurement of the affinity of peptides with the substrate by equilibrium methods. Our past results, which have been rather limited in their scope, suggested that the association of activator with substrate was an absolute requirement for LCAT activation. A new series of peptides in which we systematically vary the affinity for substrate by substitution of a number of more hydrophobic amino acids should permit us to prove this part of the activation process. We also plan to isolate large quantities of the LCAT containing lipoprotein and study its effects on model lipoproteins; one goal of this study will be to use the LCAT complex as a reagent with which we convert model nascent HDL to mature HDL. The starting nascent HDL will contain various amounts of 13C labeled lipids; their dynamic behavior will be monitored as a function of LCAT action by nuclear magnetic resonance.